1. Field of the Description
The invention concerns the temporary attachment of an object to a support, the rapid separation of the object from the support and its ejection with a precisely oriented speed, in particular to launch it without external guidance.
The invention finds an advantageous but by no means exclusive application in spacecraft such as satellites in which separation/ejection operations are needed. It can also find application in various terrestrial vehicles, maritime vehicles (surface vessels and submarines) and airborne vehicles (aircraft of all kind) in which a temporary connection is made that is to be released subsequently, possibly with immediate and precise movement of the object in question, for example to launch it with no external guidance.
A particular application of the invention is in conducting scientific experiments in the upper atmosphere or exploring the planets of the solar system using an automatic probe. For example, it can be used to secure and then release or eject a storage vessel containing a chemical substance to be used as a tracer to study winds or magnetic fields; a storage vessel of this kind can be ejected from an artificial platform such as a sounding rocket or an interplanatory probe.
2. Description of the Prior Art
Various mechanisms are already known for providing temporary attachment of this kind followed by separation and more or less forcible ejection, in practice for achieving clean separation between the object and its support.
The following documents are particularly noteworthy in this respect: U.S. Pat. No. 4,554,905, WO-82/02527, U.S. Pat. No. 3,887,150, U.S. Pat. No. 2,888,294, U.S. Pat. No. 3,196,745, U.S. Pat. No. 3,597,919, U.S. Pat. No. 4,002,120 and U.S. Pat. No. 4,187,759.
In practice these references propose the use of pressure type energy for release or separation. This energy may be pneumatic, hydraulic or pyrotechnic, for example, depending on the application. In the particularly important case of pyrotechnic energy, the pneumatic effects of combusting an explosive substance are used.
Pyrotechnic energy is also used in separator devices of the types including explosive bolts, explosive cutters or pyrotechnic release (unlatching) systems which retract an abutment member. They are usually associated with separator pistons.
Taken as a whole, the various references mentioned above are not concerned with the subsequent movement of the object.
The document FR-2 616 852 is directed to a mechanism for commanding the separation of a member from a support with which it is initially in contact. The ejection speed and acceleration are perfectly controlled. This reference teaches how to apply an accurately defined amount of energy to the object to be ejected to achieve this result.
Finally, the document FR-2 550 756 discloses a mechanism specifically designed to eject aircraft seats.
It has become clear that such mechanisms are incapable of accurately controlling the amplitude and the orientation of the ejection speed, in particular because they do not allow for manufacturing tolerances of the ejector mechanism components or the tolerances for mounting the object to its support.
The device disclosed in the document FR-2 616 852 provides a piston to eject the object by applying thrust to its base. The ejection quality depends significantly on the following parameters:
the stiffness of the parts, in particular the ejector piston and its guide members;
the accuracy with which the guide parts are manufactured and assembled;
the position of the center of mass relative to the thrust axis, with which it may be coaxial, and a main axis of inertia of the member or object to be ejected, especially if rotation about the main axis is to be imparted to the object, as is the case with the present invention; and
the quality of implementation of the abutting relationship between the piston and the member to be ejected.
Any eccentricity of the thrust axis relative to the longitudinal axis of the ejector piston, which in practice is aligned as closely as possible with the center of mass of the object, results in the application of a moment to the ejector piston which must be sufficiently stiff and must be guided extremely accurately or it will move (tilt) and impart a transverse velocity to the object.
For the guidance system to be effective it must be able to absorb any moment due to the eccentricity of the thrust axis before the object tilts too far.
Significant unwanted transverse speed can be imparted by even a small tilting movement. It is possible to quantify transverse disturbances (linear and rotational speed) according to the guidance system.
The quality of the end of travel abutment also has a very significant effect on the accuracy of subsequent movement of the object, even with objects having a high transverse inertia. This has been confirmed by experience. If the thrust axis is not accurately perpendicular to the face on the object on which the abutment bears at the end of travel, there occurs at the end of travel a tilting movement of the ejector piston which converts some of its longitudinal kinetic energy into transverse rotational energy. Some of this energy may be imparted to the object and, as already mentioned, an infinitesimal proportion of this energy is sufficient to impart significant transverse speed to the object.
It is found that the quality of the ejection is directly conditioned by the geometrical quality of the ejector and the initial distribution of clearance.
The main consequences are: delicate adjustment, inevitable and significant parameter spread and great difficulty in modeling the ejector (to take into account stiffness, clearance, impact, etc.).